X-ray diagnostic apparatus, image processing apparatus, and image processing method

ABSTRACT

According to one embodiment, an X-ray diagnostic apparatus generating an X-ray image in a region of interest, includes a radiography device and processing circuitry. The radiography device takes a first X-ray image before injection of a contrast medium, and takes a second X-ray image and a third X-ray image after injection of the contrast medium. The processing circuitry generates an output image having pixel values that are ratios of pixel values between a difference between the second X-ray image and the first X-ray image and a difference between the third X-ray image and the first X-ray image.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority of Japanese PatentApplication No. 2015-030133, filed Feb. 19, 2015, and claims the benefitof priority of Japanese Patent Application No. 2016-028954, filed Feb.18, 2016, the entire contents of all of which are incorporated herein byreference.

FIELD

Embodiments described herein relate generally to an X-ray diagnosticapparatus, an image processing apparatus, and an image processingmethod.

BACKGROUND

Tests using an X-ray diagnostic apparatus include X-ray subtractionangiography. In this test, the same site of an object is taken as animage before contrast medium injection (mask image) and an image aftercontrast medium injection (contrast image). An image (subtraction image)obtained by calculating the difference between these images isgenerated.

The subtraction image is an image in which image portions of bloodvessels are visualized with a contrast medium. A user can easily graspthe situation of bloodstreams in the object by observing the subtractionimage. For example, in the case of thrombectomy using a catheter, it isexpected to allow identification of whether bloodstreams are recoveredor not in a territory of a thrombus by observing whether image portionsof blood vessels downstream of a thrombus (i.e. vascular territory ofthe thrombus, hereinafter referred to as “territory”) appears or not inthe subtraction image after thrombectomy.

For example, in thrombectomy using a catheter for a patient of cerebralinfarction, an operation of removing a thrombus is triedpharmacologically by a thrombolytic agent released from the distal endof the catheter or mechanically by a device protruding from the distalend of the catheter. In this case, it is preferred that each time theoperation of removing a thrombus is performed, a user as a practitioneridentifies whether the bloodstream in the territory is recovered or not.This identification method may be, for example, a method ofconsecutively taking X-ray images while releasing the contrast mediumfrom the distal end of the catheter into a blood vessel, obtainingsubtraction images, and observing whether an image portion of the bloodvessel visualized in these subtraction image appears in the territory ornot.

Unfortunately, according to this method, it is difficult to determinewhether the bloodstream is restored across the entire territory on thebasis of the subtraction images. The difficulty is because the contrastmedium released from the distal end of the catheter circulates in abloodstream to leave normal brain tissue to be also visualized and thevisualized image portion is included in the subtraction images.

The present invention has an object to provide an X-ray diagnosticapparatus, an image processing apparatus, and an image processing methodcapable of generating the image that allows easy identification ofbloodstream recovery in the territory, i.e. in the region includingblood vessels downstream of a thrombus, during or after thrombectomyusing the catheter.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate embodiments of the invention, andtogether with the general description given above and the detaileddescription of the embodiments given below, serve to explain theprinciples of the invention.

FIG. 1 is a block diagram showing an example of an X-ray diagnosticapparatus according to a first embodiment of the present invention;

FIG. 2 is a schematic block diagram showing an example of functionsachievable by the processor of the processing circuitry according to thefirst embodiment;

FIG. 3 is a diagram illustrating an example of the situation of takingthe mask image M of the head of the object P;

FIG. 4A is a diagram illustrating an example of the situation of takingthe first contrast image P1 of the head of the object P;

FIG. 4B is a diagram illustrating an example of the subtraction image asa first difference image (P1−M), which can be obtained using the firstcontrast image P1 and the mask image M;

FIG. 5A is a diagram illustrating an example of the situation of takinganother first contrast image P2 of the head of the object P;

FIG. 5B is a diagram illustrating an example of the subtraction image asanother first difference image (P2−M), which can be obtained using theother first contrast image P2 and the mask image M;

FIG. 5C is a diagram illustrating an example of an image as a ratioimage 81 ((P2−M)/(P1−M)) having pixel values that are the ratios ofpixel values between the other first difference image (P2−M) and thefirst difference image (P1−M);

FIG. 6A is a diagram illustrating an example of the situation of takinga second contrast image P3 of the head of the object P;

FIG. 6B is a diagram illustrating an example of a second differenceimage (P3−M), which can be obtained using the second contrast image P3and the mask image M;

FIG. 7 is a diagram illustrating an example of a ratio image((P3−M)/(P2−M)) having pixel values that are the ratios of pixel valuesbetween the second difference image (P3−M) and the other firstdifference image (P2−M);

FIG. 8 is a flowchart showing an example of procedures of causing theCPU of the processing circuitry shown in FIG. 1 to generate an imagethat allows easy identification of bloodstream recovery downstream(territory) of a thrombus in thrombectomy using the catheter;

FIG. 9 is a block diagram showing an example of an X-ray diagnosticapparatus according to the second embodiment of the present invention;

FIG. 10 is a schematic block diagram showing a configuration example offunctions actualized by a CPU of the processing circuitry according tothe second embodiment;

FIG. 11 is a diagram illustrating an example of a situation where thepredictive ratio image (E) and the ratio image are displayed on thedisplay in parallel; and

FIG. 12 is a flowchart showing an example of procedures for causing thepredictive ratio image generating function and the second imagegenerating function to display the ratio image and the predictive ratioimage (E) on the display in parallel.

DETAILED DESCRIPTION

Hereinbelow, a description will be given of an X-ray diagnosticapparatus, an image processing apparatus, and an image processing methodaccording to embodiments of the present invention with reference to thedrawings.

In general, according to one embodiment, the X-ray diagnostic apparatusgenerating an X-ray image in a region of interest includes a radiographydevice and processing circuitry. The radiography device takes a firstX-ray image before injection of a contrast medium, and takes a secondX-ray image and a third X-ray image after injection of the contrastmedium. The processing circuitry generates an output image having pixelvalues that are ratios of pixel values between a difference between thesecond X-ray image and the first X-ray image and a difference betweenthe third X-ray image and the first X-ray image.

First Embodiment

FIG. 1 is a block diagram showing an example of an X-ray diagnosticapparatus 10 according to a first embodiment of the present invention.

As shown in FIG. 1, the X-ray diagnostic apparatus 10 includes aradiography device 11, and an image processing apparatus 12. Theradiography device 11 of the X-ray diagnostic apparatus 10 is typicallyinstalled in a laboratory, and generates X-ray projection datapertaining to a site (a region of interest) of a patient P. The imageprocessing apparatus 12, which is often installed in an operation roomadjoining the laboratory, generates X-ray images based on the projectiondata, and displays the images.

The radiography device 11 includes: an X-ray detector 21; an X-raygenerator 24 including an X-ray tube 22, and a collimator 23 for theX-ray tube 22; a C-arm 25; a bed 26; a high voltage device 27; acollimator driver 28; an arm driver 29; an injector 30; a bed driver 31;and a controller 32. The components 21 to 32 of the radiography device11 may be conventionally known components.

The X-ray detector 21 is provided at one end of the C-arm 25 opposite tothe X-ray tube 22 so as to sandwich the patient P supported on atabletop (catheter table) 33 of the bed 26. The X-ray detector 21, whichis made of a flat panel detector (FPD), detects X-rays with which theX-ray detector 21 is irradiated, and outputs X-ray projection data onthe basis of the detected X-rays. The projection data is supplied to theimage processing apparatus 12 through the controller 32. The X-raydetector 21 may include an image intensifier, a TV camera or the like.

The X-ray generator 24 is provided at the other end of the C-arm 25, andincludes the X-ray tube 22 and the collimator 23.

The X-ray tube 22 is applied with voltage by the high voltage device 27,and generates X-rays. The X-rays generated by the X-ray tube 22 areemitted toward the object P.

The collimator 23 may be, for example, an X-ray irradiation field stopmade of multiple lead blades. The collimator 23 is controlled by thecontroller 32 through the collimator driver 28, and adjusts the X-rayirradiation range irradiated with X-rays emitted from the X-ray tube 22.

The C-arm 25 holds the X-ray generator 24 and the X-ray detector 21 inan integrated manner. The C-arm 25 is controlled and driven by thecontroller 32, thereby allowing the X-ray generator 24 and the X-raydetector 21 to integrally move around the object P.

The bed 26 is installed on a floor, and holds the tabletop 33. The bed26 is controlled by the controller 32, and moves and turns (rolls) thetabletop 33 in the horizontal direction and the vertical direction.

The high voltage device 27 is controlled by the controller 32, andsupplies the X-ray tube 22 with power required for X-ray irradiation.

The collimator driver 28 is controlled by the controller 32 and adjuststhe aperture of the collimator 23, which in turn adjusts the rangeirradiated with X-rays emitted from the X-ray tube 22 according to animaging protocol.

The arm driver 29 and the bed driver 31 are controlled by the controller32, and drive the C-arm 25 and the tabletop 33, respectively.

The injector 30 is a device that is controlled by the controller 32 andinjects a contrast medium through the catheter 34 held by an operator Oand inserted into an affected area of the object P. Timing of injectingthe contrast medium and stopping the injection, and the concentrationand injection speed of the contrast medium are automatically controlledby the controller 32. The injector 30 may be prepared as an external andisolated device different from the X-ray diagnostic apparatus 10. Inthis case, the X-ray diagnostic apparatus 10 does not include theinjector 30. The injector 30 is not necessarily controlled by thecontroller 32 irrespective of whether the injector is prepared at theoutside or not. For example, an instruction by the operator O may beaccepted through an input section provided at the injector 30, and thecontrast medium may be injected at the concentration, speed and timingaccording to the instruction.

The controller 32 is controlled by the image processing apparatus 12,and in turn controls the X-ray detector 21, the high voltage device 27,the collimator driver 28, the arm driver 29, the injector 30, and thebed driver 31, thereby taking X-ray images, generating projection dataon the region of interest in the object P, and supplying the data to theimage processing apparatus 12.

On the other hand, as illustrated in FIG. 1, the image processingapparatus 12 includes an input circuit 41, a display 42, a networkconnection circuit 43, memory circuitry 44, and processing circuitry 45.The components 41 to 45 of the image processing apparatus 12 may be madeup of, for example, an information processing device, such as a typicalpersonal computer or workstation.

The input circuit 41 includes, for example, a typical input device, suchas a mouse, trackball, keyboard, touch panel, or numeric keypad, and ahand switch for instructing X-ray irradiation timing, and outputs, tothe processing circuitry 45, an operational input signal correspondingto an operation by the user. A microphone for audio input may be adoptedas the input circuit 41. In this case, the microphone converts a voiceinput by the user into a digital audio signal. The processing circuitry45 applies an audio recognition process to the digital audio signal,thereby performing an operation according to the voice input by theuser. The user may be identical to or different from the operator O.

The display 42, which may be, for example, a typical display outputdevice, such as a liquid crystal display or OLED (Organic Light EmittingDiode) display, displays various images, such as X-ray images, accordingto the control by the processing circuitry 45.

The network connection circuit 43 is embedded with various informationcommunication protocols in conformity with the geometry of a network100. The network connection circuit 43 connects the X-ray diagnosticapparatus 10 to another apparatus according to the various protocols.Here, the network 100 means an information communication network usingtelecommunication techniques, and includes not only a wireless/wired LAN(Local Area Network), such as a hospital main LAN, and the Internet, butalso a telephone communication network, an optical fiber communicationnetwork, a cable communication network, and a satellite communicationnetwork. In this embodiment, X-ray diagnostic apparatus 10 does notnecessarily include the network connection circuit 43.

The memory circuitry 44 has a configuration including memory circuitryreadable and writable by a processor of the processing circuitry 45,such as a magnetic or optical recording medium or a semiconductormemory, and is controlled by the processing circuitry 45 to store a maskimage M and the positions and the like of the X-ray tube 22 and theX-ray detector 21 at the time of taking the mask image M with referenceto the tabletop 33.

The processing circuitry 45 includes at least the processor. Theprocessing circuitry 45 comprises, for example, the processor, RAM, andmemory circuitry including ROM. The processing circuitry 45 controls theoperation of X-ray diagnostic apparatus 10, which includes thecontroller 32, according to a program stored in the memory circuitry.The processor of the processing circuitry 45 loads, onto the RAM, animage processing program, and data required to execute the programstored in the memory circuitry typified by a ROM. The configurationillustrated in the description above may be what has been conventionallyknown.

The processor of the processing circuitry 45 of this embodiment executesa process for generating an image that allows easy confirmation ofbloodstream recovery at an area downstream of a thrombus (territory)according to this image processing program, in thrombectomy using thecatheter 34.

The RAM of the processing circuitry 45, which may be what have beenconventionally used, provides a work area for temporarily storingprograms executed by the processor, and data. The memory circuitry,typified by the ROM of the processing circuitry 45, stores a bootprogram and image processing program for X-ray diagnostic apparatus 10,and various data items for executing these programs.

The memory circuitry, which is typified by ROM and may be what has beenconventionally used, has a configuration that includes memory circuitryreadable by a processor, such as a magnetic or optical recording mediumor a semiconductor memory. A part of or the entire programs and data inthe memory circuitry may be configured to be downloadable via anelectronic network. The processing circuitry 45 may be made up ofmultiple processors.

FIG. 2 is a schematic block diagram showing an example of functionsachievable by the processor of the processing circuitry 45 according tothe first embodiment.

As shown in FIG. 2, the processor of the processing circuitry 45functions at least as an imaging control function 51, a first imagegenerating function 52, a second image generating function 53, and amovement processing function 54, according to the image processingprogram. These functions are stored in the memory circuitry in forms ofrespective programs.

The imaging control function 51, which may be what has beenconventionally used, takes X-ray images before and after injection ofthe contrast medium by controlling the radiography device 11 through thecontroller 32.

The first image generating function 52 generates a digital image havingpixel values that are the logarithms of the intensity of X-rays havingpassed through the object P, on the basis of the projection data. Forexample, the first image generating function 52 generates a mask imageon the basis of projection data obtained by X-ray imaging before anoperation of removing a bloodstream obstruction, such as a plaque orthrombus, and before contrast medium injection. The first imagegenerating function 52 generates a first contrast image on the basis ofprojection data obtained by X-ray imaging before the operation ofremoving the bloodstream obstruction and after contrast mediuminjection. The first image generating function 52 generates a secondcontrast image on the basis of projection data obtained by X-ray imagingafter the operation of removing the bloodstream obstruction and aftercontrast medium injection.

Here, a conventional subtraction image is briefly described. Thefollowing description is for the case where the object P causes cerebralinfarction, the bloodstream obstruction is a thrombus, the region ofinterest including the bloodstream obstruction is the head of the objectP, and an operation of removing the bloodstream obstruction isthrombectomy using the catheter 34. The cerebral infarction is apathological condition where a cerebral artery is clogged with athrombus or the like, and no blood flows through tissue downstream ofthe artery (territory) or the flow rate of blood significantlydecreases.

A first alternative of a method of treating a cerebral infarctionpatient is administration of a thrombolytic agent into a vein. There isa limitation where the administration has to be made within a limitedtime, which varies among areas in the world. The administration has alow success rate, which is a probability that the thrombus dissolves andthe flow rate of blood is sufficiently recovered (restored).

For a case where a thrombolytic agent has been unable to be administeredinto a vein within a limited time, a case where the disease-onset timeis unknown, or a case where the thrombolytic agent has been administeredbut has been unsuccessful, the thrombectomy using the catheter 34 isperformed as a second alternative of the treatment method for a cerebralinfarction patient.

The thrombectomy using the catheter 34 is an operation of inserting thecatheter 34 into a cerebral blood vessel and removing a thrombus whileconsecutively taking X-ray images of the head of the object P (i.e.,under X-ray fluoroscopy). In thrombectomy using the catheter 34, theoperation of removing the thrombus is tried pharmacologically by thethrombolytic agent released from the distal end of the catheter 34 ormechanically by a device protruding from the distal end of the catheter34.

In the case of using the thrombolytic agent, the thrombolytic agent isreleased from the distal end of the catheter 34 and the area is left asit is awhile.

In the case of mechanically removing the thrombus, a device for wrappingthe thrombus is caused to protrude from the distal end of the catheter34, the contrast medium is released while X-ray images of the head ofthe object P are consecutively taken, the position of the thrombus isidentified, the device is inserted into the thrombus to wrap thethrombus with the device. Next, the device is extracted, therebyremoving many parts of the thrombus.

According to another method of mechanically removing a thrombus, adevice for crushing the thrombus is caused to protrude from the distalend of the catheter 34, the contrast medium is released while images ofthe head of the object P are consecutively taken, and the position ofthe thrombus is identified, the device is inserted into the thrombus.The device outputs ultrasonic waves or the like to crush the thrombus.The crushed fragments are sucked out through the catheter.

In the case of thrombectomy using the catheter 34, it is important thateach time the operation of removing a thrombus is performed, a user as apractitioner identifies whether the bloodstream in the territory isrecovered or not. It is thus preferred that X-ray images of the head ofthe object P be consecutively taken while the contrast medium be beingreleased in the artery from the distal end of the catheter 34, andobservation be made on whether a visualized vascular image appear in theterritory or not. When the thrombus is sufficiently removed, images ofarterial branches, capillary-vascular networks, and veins in theterritory appear.

The arterial branches or the capillary-vascular network in the territorymay sometimes be clogged with another thrombus. In some cases, thispathological condition may have originally occurred. In other cases,this condition may be caused because the debris of the thrombus has beencaused by the thrombectomy, flown downstream, and caused clogging. Inthese cases, only parts of the arterial branches and thecapillary-vascular networks in the territory are imaged.

For generating images for observing such types of bloodstreamsituations, it has been known that generation of a subtraction image(difference image) is effective in removing image portions caused by thecontrast medium having been dispersed in tissue, such as of the skull,or in blood.

To generate the difference image, first, the first image generatingfunction 52 generates a mask image M on the basis of projection dataobtained by X-ray imaging before the operation of removing a thrombusand before contrast medium injection. The image is generated before theoperation of removing the thrombus, and it can thus be considered that aregion 61 with no bloodstream in the cerebral artery coincides with theterritory.

FIG. 3 is a diagram illustrating an example of the situation of takingthe mask image M of the head of the object P. FIG. 4A is a diagramillustrating an example of the situation of taking the first contrastimage P1 of the head of the object P. FIG. 4B is a diagram illustratingan example of the subtraction image (first difference image) 71 (P1−M),which can be obtained using the first contrast image P1 and the maskimage M.

When the contrast medium is injected before the operation of removingthe thrombus, the region 62 upstream of the territory is stained withthe contrast medium (see the hatched region in FIG. 4A). For example,the first image generating function 52 generates the first contrastimage P1 on the basis of the projection data obtained by taking X-rayimages while releasing the contrast medium from the distal end of thecatheter 34 into the artery. Preferably, the first contrast image P1 isgenerated on the basis of the projection data obtained by taking X-rayimages after a lapse of time during which the contrast medium isuniformly distributed across tissue after administration of the contrastmedium.

The second image generating function 53 generates the first differenceimage 71 (P1−M) with pixel values that are the differences between thepixel values of the pixels of the first contrast image P1 and the pixelvalues of the pixels of the mask image M (see FIG. 4B).

As shown in FIG. 4B, the pixels corresponding to the territory in thefirst difference image 71 (P1−M) do not have uniform pixel values. Thisnonuniformity is because the X-ray transparent length for the contrastmedium having dispersed in the object P varies according to thepositions of the pixels.

For example, when the contrast medium is injected through the catheterin the artery, the blood vessel, the blood vessel branches downstream ofthe vessel, capillary-vascular networks in the territory downstream ofthe branches, and the veins downstream of the networks are visualized.At this time, the capillary-vascular networks are very fine and thenumber of networks is significantly large. Consequently, the networkscannot be individually viewed but appear as if they were cloud. When thecapillary-vascular networks in the territory are uniformly visualized,the pixels corresponding to the first difference image 71 (P1−M) in theterritory have uniform pixel values according to use of images taken bythe X-ray CT apparatus. However, as to images taken by the X-raydiagnostic apparatus 10, the X-ray transparent length for the contrastmedium dispersing over the object P varies with the pixel positions.Consequently, the attenuating effect due to the contrast medium varieswith the pixel positions. Thus, even if the capillary-vascular networksin the territory are uniformly visualized, the portions corresponding tothe territory of the first difference image 71 (P1−M) generated by theX-ray diagnostic apparatus 10 are not uniform (see FIG. 4B).

FIG. 5A is a diagram illustrating an example of the situation of takinganother first contrast image P2 of the head of the object P. FIG. 5B isa diagram illustrating an example of the subtraction image (anotherfirst difference image) 72 (P2−M), which can be obtained using the otherfirst contrast image P2 and the mask image M. FIG. 5C is a diagramillustrating an example of an image (hereinafter, referred to as a ratioimage) 81 ((P2−M)/(P1−M)) having pixel values that are the ratios ofpixel values between the other first difference image 72 (P2−M) and thefirst difference image 71 (P1−M).

For example, the contrast medium for taking the first contrast image P1is dispersed in the blood. Consequently, when the first contrast imageP2 is taken again, this image is thus taken in the state with anincreased contrast medium concentration (the amount of contrast mediumcontained in living tissue having a unit volume) that is higher thanthat for P1. In this case, as with the first difference image 71 (P1−M),the other first difference image 72 (P2−M) have pixels corresponding tothe territory that do not have uniform pixel values (see FIG. 5B).

Thus, even if there is a region where restoration of the bloodstream(the clogging of the blood vessel is removed, and the flow rate of bloodis sufficiently recovered) due to thrombectomy increases the contrastmedium concentration (the amount of contrast medium contained in theliving tissue having a unit volume), it is difficult to identify theregion due to nonuniformity of the pixel values of the portionscorresponding to the territory through the difference images 71 and 72.It is thus difficult to determine whether the thrombectomy has succeededor not. Even if the difference image ((P1−M)−(P2−M))=(P1−P2) between thefirst difference image 71 (P1−M) and the other first difference image 72(P2−M) is generated, each of the pixels of the portions corresponding tothe territory in the difference image (P1−P2) do not have unique pixelvalue because the contrast medium concentrations (the amount of contrastmedium contained in living tissue having a unit volume) in thedifference images 71 and 72 are different from each other.

The second image generating function 53 of the X-ray diagnosticapparatus 10 according to this embodiment generates a ratio image havingpixel values that are the ratios of pixel values between the differenceimages. The ratio image generated from between the difference images isan image in which the ratios of the contrast medium concentration (theamount of contrast medium in living tissue having a unit volume) at thetime of imaging in the contrast images of the difference images arereflected. Consequently, the pixels of the portions corresponding to theterritory in the ratio image have substantially uniform pixel values.

For example, as shown in FIG. 5C, the ratio image 81 ((P2−M)/(P1−M))having pixel values that are the ratios of the pixel values of thepixels of the other first difference image 72 (P2−M) and the pixelvalues of the pixels of the first difference image 71 (P1−M) is an imagein which only increase in contrast medium concentration (the amount ofcontrast medium contained in living tissue having a unit volume) isreflected, and is an image having a uniform portion corresponding to theterritory (see FIG. 5C).

FIG. 6A is a diagram illustrating an example of the situation of takinga second contrast image P3 of the head of the object P. FIG. 6B is adiagram illustrating an example of a second difference image 73 (P3−M),which can be obtained using the second contrast image P3 and the maskimage M.

FIG. 7 is a diagram illustrating an example of a ratio image 82((P3−M)/(P2−M)) having pixel values that are the ratios of pixel valuesbetween the second difference image 73 (P3−M) and the other firstdifference image 72 (P2−M). An image portion 66 in FIG. 7 is an exampleof an image portion caused by X-rays having passed through a region 63,a region 62 and a region 61 (see FIG. 6A). In FIG. 7, the image portion67 is an example of an image portion generated by X-rays having passedthrough only the region 63, while the image portion 68 is an example ofan image portion generated by X-rays having passed through the regions63 and 62. Alternatively, instead of the other first difference image 72(P2−M) in FIGS. 6B and 7, the first difference image 71 (P1−M) may beused.

The case is considered where the operation of removing a thrombus allowsa bloodstream recovered at a part of the territory. In this case, whenthe contrast medium is injected after the operation of removing thethrombus, the region 63 in FIG. 6A where the bloodstream is recovered isstained with the contrast medium but no contrast medium enters theregion 61 in FIG. 6A where the bloodstream is not recovered.

At this time, first, the second image generating function 53 generatesthe second difference image 73 (P3−M) with pixel values that are thedifferences between the pixel values of the pixels of the secondcontrast image P3 and the pixel values of the pixels of the mask image M(see FIG. 4B). However, as with the other first difference image 72(P2−M) and the first difference image 71 (P1−M), the second differenceimage 73 (P3−M) is an image with the pixels of a portion correspondingto the territory that have nonuniform pixel values (see FIG. 6B).

Subsequently, the second image generating function 53 generates a ratioimage 82 ((P3−M)/(P2−M) (or (P3−M)/(P1−M))) having pixel values that arethe ratios between the pixel values of pixels of the second differenceimage 73 (P3−M) and the pixel values of pixels of the other firstdifference image 72 (P2−M) (or a first difference image 71 (P1−M)).

The second difference image 73 (P3−M) shown in FIG. 6B is an image withpixels of the portion corresponding to the territory that arenonuniform. Consequently, even if the region 63 with the contrast mediumconcentration (the amount of contrast medium contained in living tissuehaving a unit volume) being high due to recovery of the bloodstreamexists, it is difficult to determine the region 63 owing to adverseeffects of nonuniformity of pixel values of pixels of the portioncorresponding to the territory only by comparison between FIGS. 6B and5B.

On the other hand, as shown in FIG. 7, according to the ratio image 82,there is no increase in bloodstream between the second difference image73 (P3−M) and the other first difference image 72 (P2−M) at the imageportion 67 generated by X-rays having passed through the region 62 inFIG. 6A which is corresponding to upstream of the thrombus, but only thecontrast medium concentration (the amount of contrast medium containedin living tissue having a unit volume) varies. Consequently, the imageportion 67 has a substantially identical pixel value “a” over the entireregion. Meanwhile, the pixels corresponding to the image portion 68generated by X-rays having passed through the region 63 in FIG. 6A wherethe bloodstream is recovered have pixel values in which increase incontrast medium concentration due to increase in bloodstream isreflected in the second difference image 73 (P3−M), in comparison withthe other first difference image 72 (P2−M). Consequently, the pixels ofthe image portion 68 have a pixel value “b”, which is different fromthat of the pixels of the image portion 67.

The ratio between the pixel value “a” and the pixel value “b” isapproximately proportional to the magnitude obtained by multiplying thethickness of the portion where the bloodstream is recovered by theamount of contrast medium in the blood contained in the portion. Forexample, if the territory covers approximately half of the brain,recovery across the entire territory causes the pixel value “b” to beapproximately twice as high as the pixel value “a”.

Thus, the ratio image 82 becomes an image representing a region wherethe bloodstream is recovered by thrombectomy performed between takingthe first contrast image P1 or the other first contrast image P2 andtaking the second contrast image P3. Consequently, the user can easilyand securely grasp the bloodstream restored region by observing theratio image 82. An image of the territory obtained by another modality,such as an X-ray CT (Computed Tomography) apparatus or a magneticresonance imaging (MRI) apparatus is compared with the ratio image 82and observed, thereby allowing the user to obtain information on therestored region in more detail.

The mask image M, the first contrast images P1 and P2, and the secondcontrast image P3 are computed assuming that each pixel value reflectsthe X-ray fluorescence intensity at the same position. Consequently, itis preferred that the images be from the same viewpoint.

The movement processing function 54 causes the memory circuitry 44 tostore the positions of the X-ray tube 22 and the X-ray detector 21 withreference to the tabletop 33 at the time of taking the mask image M, andthis mask image M. The movement processing function 54 moves the X-raytube 22 and the X-ray detector 21 to the positions stored in the memorycircuitry 44 at the time of taking the first contrast images P1 and P2,and the second contrast image P3 such that the first contrast images P1and P2, and the second contrast image P3 should be from the sameviewpoint.

For reducing the adverse effects and the like due to the body motion ofthe object P, the movement processing function 54 finely adjusts thepositions of the X-ray tube 22 and the X-ray detector 21 through aprocess of matching the X-ray fluoroscopic image with an the mask imageM at the positions after movement such that the X-ray fluoroscopic imageshould be from the same viewpoint as that of the mask image M. Varioustypes of matching processes have been conventionally known in thetechnical field of image processing. Any of the types may be adopted.The imaging control function 51 then takes the first contrast images P1and P2, and the second contrast image P3 after the fine adjustment. Themovement processing function 54 allows the first contrast images P1 andP2 and the second contrast image P3, and the mask image M to beconfigured from the same viewpoint.

The movement processing function 54 may cause the memory circuitry 44 tostore the positions of the X-ray tube 22 and the X-ray detector 21 withreference to the tabletop 33 and the mask image M at the time of takingthe mask image M according to an instruction for “storing” issued by theuser through the input circuit 41. When an instruction for“reproduction” is issued by the user through the input circuit 41 at thetime of taking the first contrast images P1 and P2, and the secondcontrast image P3, the positions of the X-ray tube 22 and the X-raydetector 21 may be adjusted such that the first contrast images P1 andP2 and the second contrast image P3 may be configured to be from thesame viewpoint as that of the mask image M according to the instruction.

Next, an example of the operation of the X-ray diagnostic apparatus 10according to this embodiment is described.

FIG. 8 is a flowchart showing an example of procedures of causing theCPU of the processing circuitry 45 shown in FIG. 1 to generate an imagethat allows easy identification of bloodstream recovery downstream of athrombus (territory) in thrombectomy using the catheter 34. In FIG. 8,each step of the flowchart is represented by a symbol S assigned anumeral.

First, in step S1, the first image generating function 52 generates themask image M. Next, in step S2, the movement processing function 54accepts the instruction for “storing” from the user through the inputcircuit 41. Steps S1 and S2 may be simultaneously performed in parallel.Alternatively the order may be inverted.

Next, in step S3, the movement processing function 54 causes the memorycircuitry 44 to store the mask image M and the positions of the X-raytube 22 and the X-ray detector 21 with reference to the tabletop 33 atthe time of taking the mask image M.

Next, in step S4, the imaging control function 51 injects the contrastmedium into the object P through the injector 30. Next, in step S5, themovement processing function 54 accepts the instruction for“reproduction” from the user through the input circuit 41. Steps S4 andS5 may be simultaneously performed in parallel. Alternatively, the ordermay be inverted.

Next, in step S6, the movement processing function 54 adjusts thepositions of the X-ray tube 22 and the X-ray detector 21 with referenceto the tabletop 33 so as to cause the images from the same viewpoint asthat of the mask image M to be generated.

Next, in step S7, the first image generating function 52 generates thefirst contrast image P1.

Next, in step S8, the operator O performs an operation of removing abloodstream obstruction using the catheter 34.

Next, in step S9, the movement processing function 54 accepts theinstruction for “reproduction” from the user through the input circuit41.

Upon receipt of this instruction, in step S10, the movement processingfunction 54 adjusts the positions of the X-ray tube 22 and the X-raydetector 21 with reference to the tabletop 33 so as to cause the imagesfrom the same viewpoint as that of the mask image M to be generated.

Next, in step S11, the imaging control function 51 injects the contrastmedium into the object P through the injector 30. The first imagegenerating function 52 then generates the second contrast image P3.

Next, in step S12, the second image generating function 53 generates aratio image 82 ((P3−M)/(P1−M) (or (P3−M)/(P2−M))) having pixel valuesthat are the ratios between the pixel values of pixels of the seconddifference image 73 (P3−M) and the pixel values of pixels of the firstdifference image 71 (P1−M) (or the other first difference image 72(P2−M)), and displays the generated image on the display 42 (see FIG.7).

The above procedures can generate the ratio image 82 that allows easyidentification of bloodstream recovery downstream of the thrombus(territory), and display this image during or after thrombectomy usingthe catheter 34.

The X-ray diagnostic apparatus 10 including the image processingapparatus 12 according to this embodiment can thus generate the ratioimage 82. According to the ratio image 82, there is no increase inbloodstream at the image portion 67 generated by X-rays having passedonly through the region 62 upstream of the thrombus between the seconddifference image 73 (P3−M) and the first difference image 71 (P1−M), butonly the contrast medium concentration (the amount of contrast mediumcontained in living tissue having a unit volume) varies. Consequently,the image portion 67 has a substantially identical pixel value “a”across the entire region. Meanwhile, at the image portion 68 generatedby X-rays having passed through the region 63 where the bloodstream isrecovered, the bloodstream has increased in the second difference image73 (P3−M) in comparison with the first difference image 71 (P1−M).Consequently, the pixels of the image portion 68 have various pixelvalues “b” different from those of the image portion 67.

Consequently, the X-ray diagnostic apparatus 10 allows the user toeasily and securely grasp the bloodstream restored region by observingthe ratio image 82.

In general, thrombectomy using the catheter 34 requires repeatedlytaking X-ray images while releasing the contrast medium from thecatheter 34 for the sake of an operation of inserting and advancing thecatheter 34 to a site of a thrombus and an operation of removing thethrombus.

The contrast medium is dissolved in the blood and circulates over theentire body, a part of the contrast medium in the blood is graduallyfiltered by kidneys and excreted. Consequently, the contrast mediumconcentration in the blood very slightly decreases. However, in thethrombectomy using the catheter 34, the contrast medium is frequentlyand repeatedly released. Consequently, the increase in contrast mediumconcentration in the blood far exceeds the amount of decrease due tofiltration. Note that the contrast medium has a side effect of affectingthe renal function. Consequently, even for patients having a normalrenal function, the total amount of usable contrast medium is limitedwith an upper limit. In particular, for patients having a renal functiondisorder, a side effect of significantly worsening the renal functiondisorder is caused by the contrast medium.

Consequently, the upper limit of the usable contrast medium should bestrictly restricted. In other words, the operator O is imposed to decideto select one between two ways. According to one way, the sufficienttherapy for the cerebral infarction is abandoned, which causesdisorders, such as in movement and sensation, even if the life can besaved, and in turn causes the necessity of long-term rehabilitation.According to the other way, the renal function disorder is worsened,which causes the necessity of persistent dialysis or renaltransplantation.

In consideration of this point, according to the X-ray diagnosticapparatus 10 according to this embodiment, the user can significantlyeasily grasp whether the bloodstream is recovered in the territory ornot through observation of the ratio image 82. Consequently, thisapparatus can significantly reduce the amount of use of the contrastmedium in comparison with the conventional technique that simplycompares the first difference image 71 and the second difference image73 with each other.

Second Embodiment

Next, a second embodiment of the present invention, an X-ray diagnosticapparatus, an image processing apparatus, and an image processing methodaccording to the present invention are described.

FIG. 9 is a block diagram showing an example of an X-ray diagnosticapparatus 10A according to the second embodiment of the presentinvention.

The X-ray diagnostic apparatus 10A according to the second embodiment isdifferent from the X-ray diagnostic apparatus 10 according to the firstembodiment in that the apparatus 10A generates a predictive ratio image90 of a ratio image 82 through simulation. The other configurationelements and operations are not different from those of the X-raydiagnostic apparatus 10 shown in FIG. 1 in a practical view.Consequently, the same configuration elements are assigned the samesymbols. The description thereof is omitted.

The X-ray diagnostic apparatus 10A obtains volume data (medicalthree-dimensional image data) on the region of interest of the object Pfrom a modality 101 or an image server 102 connected via the network100, and causes the memory circuitry 44 to preliminarily store the data.A part of or the entire data stored in the memory circuitry 44 may beconfigured to be downloaded via the network 100, or stored through aportable memory medium, such as an optical disk.

The modality 101 is, for example, a medical image diagnostic apparatus,such as an X-ray CT (Computed Tomography) apparatus, an MRI (MagneticResonance Imaging) apparatus, an ultrasonic diagnostic apparatus, or anX-ray diagnostic apparatus, and may be any apparatus that can generatevolume data (medical three-dimensional image data) on the basis of theprojection data obtained through imaging of the object P (patient).

The image server 102 is, for example, a server that is provided for aPACS (Picture Archiving and Communication System) and is for long-termstorage of images. This server stores a reconstructed image or volumedata generated by the modality 101 connected via the network 100.

FIG. 10 is a schematic block diagram showing a configuration example offunctions actualized by a CPU of the processing circuitry 45A accordingto the second embodiment. These achieved functions may be made up ofhardware logics, such as circuits, instead of the CPU.

A volume data obtaining function 56 obtains volume data on the region ofinterest of the object P. The data is preliminarily stored in the memorycircuitry 44, or obtained from the modality 101 or the image server 102via the network connection circuit 43 and the network 100.

A predictive ratio image generating function 57 generates a predictiveimage of the first difference image 71 (predictive first differenceimage) through simulation using the volume data on the region ofinterest. The predictive ratio image generating function 57 generates apredictive image of the second difference image 73 (predictive seconddifference image) predicted to be obtained in the case where thebloodstream obstruction is completely removed, through simulation usingthe volume data on the region of interest.

Furthermore, the predictive ratio image generating function 57 generatesa predictive ratio image 90 (E) having pixel values that are the ratiosof pixel values between the predictive second difference image and thepredictive first difference image.

FIG. 11 is a diagram illustrating an example of a situation where thepredictive ratio image 90 (E) and the ratio image 82 are displayed onthe display 42 in parallel.

The second image generating function 53A according to this embodimentdisplays the ratio image 82 generated on the basis of the projectiondata obtained by taking X-ray images of the region of interest of theobject P (see FIG. 7), and the predictive ratio image 90 (E) generatedby the predictive ratio image generating function 57, on the display 42in parallel (see FIG. 11).

The predictive ratio image 90 (E) is the ratio image 82 predicted to beobtained in the case where the bloodstream obstruction is completelyremoved. Consequently, the user can easily identify the bloodstreamrestoration site and the degree of restoration by comparing andobserving the ratio image 82 and the predictive ratio image 90 (E) witheach other.

The second image generating function 53A may generate a comparisonassistance image having pixel values that are the ratios of the pixelvalues of pixels of the predictive ratio image 90 (E) and the pixelvalues of pixels of the ratio image 82, and display the image on thedisplay 42. The comparison assistance image is an image where onlyportions having not been restored are extracted. Consequently, the usercan easily identify the bloodstream restoration site and the degree ofrestoration through observation of the comparison assistance image. Itis the matter of course that the second image generating function 53Amay display all the ratio image 82, the predictive ratio image 90 (E)and the comparison assistance image on the display 42 in parallel.

The simulation using the volume data by the predictive ratio imagegenerating function 57 is herein described. Note that the predictiveratio image generating function 57 should generate the predictive firstdifference image and the predictive second difference image throughcalculation based on the volume data on the region of interest so as toconfigure the predictive ratio image 90 (E) to be configured from thesame viewpoint as that of the ratio image 82.

First, the predictive ratio image generating function 57 extracts afocal portion of cerebral infarction by an appropriate image processingor a manual operation, from the volume data generated by the X-ray CTapparatus or the MRI apparatus obtained by the volume data obtainingfunction 56. This function 57 resultantly generates the volume data Lincluding voxels each having a value to which “true (1)” is set when thevoxel position (x, y, z) corresponds to the cerebral infarction site and“false (0)” is set when the position does not correspond.

L(x, y, z)=(1 (true) if the (x, y, z) corresponds to the cerebralinfarction site, 0 (false) if not)

This function further extracts a portion corresponding to cerebralparenchyma from the same volume data, and resultantly generates volumedata B including voxels each having a value to which “true (1)” is setwhen the voxel position (x, y, z) corresponds to the cerebral parenchymaand “false (0)” is set when the position does not correspond.

B(x, y, z)=(1 (true) if the (x, y, z) corresponds to the cerebralparenchyma, 0 (false) if not)

The function performs a set operation using the volume data L and thevolume data B, and generates volume data (B

L) including voxels each having a value to which “1” is set when thedata L has a value “0” and the data B has a value “1” at the voxelposition, and “0” is set in the other cases.(B

L)(x,y,z)=B(x,y,z)(1−L(x,y,z))

The amount of blood in normal brain tissue is substantially identicalacross the tissue. However, to speak more correctly, the amount issmaller in white matter and larger in gray matter. Volume data S wherean image has been taken by an X-ray CT apparatus or an MRI apparatuswithout contrast medium, and visualized volume data T where an image hasbeen taken with the contrast medium substantially uniformly distributingin the blood are then obtained. Volume data X representing the contrastmedium concentration distribution in the brain is created from adifference image between the data T and the data S.

Here, the logical multiplication between (B

L) and X on each voxel is assumed as follows.U(x,y,z)=(B

L)(x,y,z)X(x,y,z)

U is substantially proportional to the contrast medium concentrationdistribution before restoration from cerebral infarction.

The logical multiplication between B and X on each voxel is assumed asfollows.V(x,y,z)=B(x,y,z)X(x,y,z)

V is approximately proportional to the contrast medium concentrationdistribution after complete restoration from cerebral infarction.

There is an easier method which does not consider the fact that innormal brain tissue, the amount of blood is smaller in the white matterand larger in the gray matter and assumes X to have a certain valueeverywhere. In this case, B, L and (B

L) can be created on the basis of volume data taken by the X-ray CTapparatus and the MRI apparatus without using the contrast medium.

Simulation is made on what image is obtained in the case of X-rayimaging in the same direction as that in the case of imaging the objectP, through calculation using U, which can generate an image (predictivefirst difference image) that predicts the first difference image (P2−M).An analogous process using V can generate an image (predictive seconddifference image) that predicts the second difference image (P3−M) inthe case of complete restoration from cerebral infarction. On the basisof these predictive images, the predictive ratio image 90 (E) can becalculated.E=“predictive image for (P3−M)”/“predictive image for (P2−M)”

Next, an example of the operation of the X-ray diagnostic apparatus 10Aaccording to this embodiment is described.

FIG. 12 is a flowchart showing an example of procedures for causing thepredictive ratio image generating function 57 and the second imagegenerating function 53A to display the ratio image 82 and the predictiveratio image 90 (E) on the display 42 in parallel. The procedures startafter the ratio image 82 (see FIG. 7) is generated on the basis of theprojection data obtained by X-ray imaging of the region of interest ofthe object P according to the series of procedures shown in FIG. 8.

In step S21, the predictive ratio image generating function 57 simulateswhat image is obtained in the case of X-ray imaging in the samedirection as that in the case of imaging the object P, throughcalculation using the volume data U, which can thereby generate an image(predictive first difference image) that predicts the first differenceimage (P2−M).

Next, in step S22, the predictive ratio image generating function 57simulates what image is obtained in the case of X-ray imaging in thesame direction as that in the case of imaging the object P, throughcalculation using the volume data V, which can thereby generate an image(predictive second difference image) that predicts the second differenceimage (P3−M).

Next, in step S23, the predictive ratio image generating function 57generates a predictive ratio image 90 (E) having pixel values that arethe ratios between the pixels of the predictive first difference imageand the pixels of the predictive second difference image.

In step S24, the second image generating function 53A displays the ratioimage 82 generated on the basis of the projection data obtained bytaking X-ray images of the region of interest of the object P (see FIG.7), and the predictive ratio image 90 (E) generated by the predictiveratio image generating function 57, on the display 42 in parallel (seeFIG. 11).

The above procedures can display the ratio image 82 and the predictiveratio image 90 (E) on the display 42 in parallel.

The X-ray diagnostic apparatus 10A including the image processingapparatus 12 according to the second embodiment can also exertadvantageous effects equivalent to those of the X-ray diagnosticapparatus 10 according to the first embodiment.

The X-ray diagnostic apparatus 10A according to the second embodimentcan generate the predictive ratio image 90 (E) that is the ratio image82 predicted to be obtained in the case where the bloodstreamobstruction has been completely removed, and display this image and theratio image 82 on the display 42 in parallel. Consequently, the X-raydiagnostic apparatus 10A allows the user to easily identify thebloodstream restoration site and the degree of restoration. Furthermore,in the case of generating the comparison assistance image having pixelvalues that are each the difference of each pixel of the predictiveratio image 90 (E) and each pixel of the ratio image 82 and displayingthis image on the display 42, the user can further easily identify thebloodstream restoration site and the degree of restoration.

Any one of the aforementioned embodiments can generate the image thatallows easy identification of bloodstream recovery in the territoryduring or after thrombectomy using the catheter 34.

The processing circuitry in the above-described embodiments is anexample of the processing circuitry described in the claims. Inaddition, the term “processor” used in the explanation in theabove-described embodiments, for instance, a circuit such as a dedicatedor general-purpose CPU (Central Processing Unit), a dedicated orgeneral-purpose GPU (Graphics Processing Unit), an ASIC (ApplicationSpecific Integrated Circuit), a programmable logic device including anSPLD (Simple Programmable Logic Device) and a CPLD (Complex ProgrammableLogic Device) as examples, and an FPGA (Field Programmable Gate Array).A processor implements various types of functions by reading outprograms stored in the memory circuit and executing the programs.

In addition, programs may be directly installed in the circuit of aprocessor instead of storing programs in the memory circuit. In thiscase, the processor implements various types of functions by reading outprograms stored in its own circuit and executing the programs. Moreover,each function of the processing circuitry may be implemented byprocessing circuitry configured of a single processor. Further, theprocessing circuitry may be configured by combining plural processorsindependent of each other so that each function of the processingcircuitry is implemented by causing each processor to execute thecorresponding program. When plural processors are provided for theprocessing circuitry, a memory circuit for storing the programs may beprovided for each processor or one memory circuit may collectively storeall the programs corresponding to all the processors.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the inventions.

The invention claimed is:
 1. An X-ray diagnostic apparatus generating anX-ray image in a region of interest, comprising: a radiography deviceconfigured to take a first X-ray image before injection of a contrastmedium, take a second X-ray image after the injection of the contrastmedium and before a thrombectomy is performed, and take a third X-rayimage after the injection of the contrast medium and after thethrombectomy is performed; and processing circuitry configured togenerate an output image having pixel values that are ratios of (1) adifference between pixels values of the second X-ray image and the firstX-ray image, and (2) a difference between pixel values of the thirdX-ray image and the first X-ray image.
 2. The X-ray diagnostic apparatusaccording to claim 1, wherein the output image indicates a region wherea bloodstream is recovered by the thrombectomy performed between thetaking of the second X-ray image and the taking of the third X-rayimage.
 3. The X-ray diagnostic apparatus according to claim 2, whereinthe thrombectomy is performed multiple times, and the processingcircuitry is further configured to generate and update the output imagefor each time the thrombectomy is performed.
 4. The X-ray diagnosticapparatus according to claim 1, further comprising: a memory storing afirst imaging position pertaining to an X-ray tube and an X-ray detectorat a time of taking the first X-ray image, and wherein the processingcircuitry is further configured to move the X-ray tube and the X-raydetector to the first imaging position based on an instruction by auser.
 5. The X-ray diagnostic apparatus according to claim 4, whereinthe processing circuitry is further configured to cause the memory tostore the first X-ray image and the first imaging position of the X-raytube and the X-ray detector with reference to a tabletop, at the time oftaking the first X-ray image according to the instruction by the userthrough an input circuit; and move the X-ray tube and the X-ray detectorto the first imaging position so as to cause the second X-ray image andthe third X-ray image to be images from a viewpoint identical to that ofthe first X-ray image, at respective times of taking the second X-rayimage and taking the third X-ray image, according to the instruction bythe user through the input circuit.
 6. The X-ray diagnostic apparatusaccording to claim 1, wherein the radiography device is furtherconfigured to take the second X-ray image after a lapse of time duringwhich the contrast medium is uniformly distributed across tissue afterthe injection of the contrast medium.
 7. An image processing apparatusgenerating an X-ray image in a region of interest, comprising:processing circuitry configured to generate a first X-ray image based onan imaging before injection of a contrast medium, a second X-ray imagebased on an imaging after the injection of the contrast medium andbefore a thrombectomy is performed and a third X-ray image based on animaging after the injection of the contrast medium and after thethrombectomy is performed; and generate an output image having pixelvalues that are ratios of (1) a difference between pixel values of thesecond X-ray image and the first X-ray image, and (2) a differencebetween pixel values of the third X-ray image and the first X-ray image.8. An image processing method of an image processing apparatusgenerating an X-ray image in a region of interest, the methodcomprising: generating a first X-ray image based on an imaging beforeinjection of a contrast medium, a second X-ray image based on an imagingafter the injection of the contrast medium and before a thrombectomy isperformed, and a third X-ray image based on an imaging after theinjection of the contrast medium and after the thrombectomy isperformed; and generating an output image having pixel values that areratios of (1) a difference between pixel values of the second X-rayimage and the first X-ray image, and (2) a difference between pixelvalues of the third X-ray image and the first X-ray image.